Ireland, for example, has committed $58.3m over five years to Mozambique. Canada has also agreed to be a commit funds.

The four African nations have each secured additional funds from other sources, including the World Bank and the Global Fund to Fight AIDS, Tuberculosis and Malaria.

Cutting costs

Analysts say the companies are able to provide the drugs at cheaper prices by cutting marketing and distribution costs because the treatments are so well known there is no need for them to be advertised.

Profits from drugs used for other ailments not related to Aids can also used to offset the cost of providing cheaper Aids treatments. In addition, already existing drugs do not have the burden of large research and development expenses.

The high cost of anti-retroviral drugs is a big issue in poor countries, with campaigners often arguing that drug companies' profit margins are too large.

In southern Africa, only 50,000 out of four million Aids sufferers are receiving required treatment.

'Crucial breakthrough'

Aids campaigners have welcomed Mr Clinton's initiative as an important step forward.

"Providing Aids treatment to those who most urgently need it in poor countries is the most urgent health challenge the world faces," said Dr Lee Jong-Wook, director of the World Health Organization.

Irish rock star Bono, a leading Aids activist, said the deal "marks a crucial breakthrough in the Aids emergency, showing that we can, and must, wage a successful war against this preventable and treatable disease".